These biscuits are both gluten-free and dairy-free, but deliciously tender on the inside and crisp along the edges. Serve them up for breakfast with butter and jam or alongside a steaming bowl of soup.
Combine flours with xanthan gum and whisk to evenly combine. Using a pastry cutter, cut coconut oil into flour mixture until it becomes crumbly with the coconut oil reaching the size of a small pea.
In a small bowl, beat the egg, then whisk in the coconut milk and sourdough starter. Pour this into the flour mixture and mix with a fork until a dough begins to form. Now knead the dough with your hands in the bowl until it comes together in a cohesive mass. The dough may be sticky at this point.
Cover the dough and allow to sour for 4 to 12 hours. At first there will be no noticeable tang, then the dough will develop to produce a noticeable sourdough flavor.
When ready to bake, preheat the oven to 425°F. Sprinkle the baking powder, baking soda, and salt over the biscuit dough. Knead this in for a couple of minutes by folding the dough over itself over and over again.
Once the dry ingredients are incorporated, sprinkle a work surface with tapioca flour. Move the dough to the floured surface and sprinkle more tapioca flour over it if the dough is quite sticky. Knead this a few times, adding more flour as needed, forming a slightly sticky yet cohesive dough.
Pat the dough out into a circle 1 inch high. Cut the dough into eight triangular biscuits or use a biscuit cutter to cut biscuits as desired.
Carefully transfer these to a cast-iron skillet or baking sheet. The dough will still be fragile so treat it gently. Leave 1 to 2 inches of space between biscuits as they will expand.
Bake 12-15 minutes, or until lightly brown. As they are gluten and dairy-free, these biscuits may not turn as golden brown as traditional wheat biscuits. Remove to cooling rack and cool five minutes before serving.